Leopard frogs, Rana pipiens, from the northcentral United States have been an exceedingly valuable resource for teaching and research in the biomedical sciences. Leopard frogs, unlike the laboratory mouse, have been obtained from natural populations. The numbers of these frogs available to the biomedical research community have dwindled drastically and the health of those which are available has not been good. Our objectives of this study are to identify the causes of the reduction in populations and to ascertain what is in the environment that is affecting the health of afflicted frogs. We believe that this information is of crucial importance if natural populations are ever to be restored. We also believe that identification of environmental insults to the health of frogs will be essential for success of both outdoor culture and colony husbandry procedures. The geographic regions chosen for study include conifer forests, hardwood forests, and grassland habitats. Characterization of plant communities, water chemistry, population density, Aeromonas hydrophila infections, and carcass pesticide levels will be undertaken. Reproductive competence of frogs throughout the varied habitats will be measured.